I think Stalin is quite popular in Russia. It would be quite surprising if Stalin was not that popular. The popularity of Stalin today may be even greater than it was in 1970s and 1980s. There are multiple reasons.
First of all, Stalin is credited for winning the Great Patriotic War, the most bloody war in human history and the history of Russia. Many people are aware that should the USSR fail, the majority of the population would be exterminated. I think this alone is quite sufficient.
The Stalin's rule was marked with the height of Russia's power and worldwide influence, including the largest and the most powerful army in the world (and in the whole history up to this day), the creation of socialist system, the founding of the United Nations.
Stalin is often perceived as a good diplomat that could conduct successful negotiations with even ideological enemies as opposed to the latter leaders who either conceded positions without compensation "for friendship" or openly and dangerously conflicted. In this light very often excerpts from Churchill's memoirs praising Stalin are cited as a proof that even rivals respected him.
The Stalin's era is marked with serious scientific and cultural achievements. The rate of economic growth in the pre-war USSR was greater than elsewhere in the world, including the modern China. This is positively contrasted with the epoch of Brezhnev's stagnation. He is credited for creating the Russian atomic bomb, aviation, the exploration of the Arctic, building Moscow metro. Russian cinematography, music and architecture also achieved heights under Stalin.
Stalin is often compared to the previous and later leaders. He is remembered for constantly decreasing prices after the war compared to the later Soviet periods when the prices often were rising. The quality of production under Stalin was much greater than in the later times, especially under Khrushchev when quantity was emphasized. This includes the food quality and house building. Stalin-era buildings in Moscow are currently priced much greater than those from post-Stalin epoch in retail market. Stalin-era ornate metro station design is remarkably different from purely functional deign of Khrushchev's
Stalin is often claimed to take necessary measures to strengthen the state internally and prevent its breakup. In this light the repressions are viewed as a positive preventive measures. This is often compared to the negative processes that surfaced after Krushchev's and Gorbachev's liberalizations that eventually led to the breakup of the USSR.
It should be noted that Stalin is often praised not only by Communists but also by various nationalists and monarchists who perceive Stalin as a kind of strong and just "Tsar". The monarchists for example, frequently believe that Stalin was in fact Orthodox Cristian and sought to protect the church. This is based on the fact of the war-time reconciliation with the church by the Stalin's government to appeal to the patriotic feelings o the population. They also sometimes praise Stalin for purging the leadership of the party of Jews who are considered unpatriotic and anti-Russian. They often oppose him to revolutionary destructors, which they allege were at power before him.
It should be also noted that the popularity of Stalin rose considerably in post-Soviet years compared to that of the late USSR along with popular anti-Americanism due to evident crude influence of the USA and the West in Russian politics that detrimented the wealth of the people and strength of the state.
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In this video a Russian philosopher and politologist Alexander Dugin explains his point of view on the reasons of popularity of Stalin: http://www.youtube.com/watch?v=URDsT6HXRhQ . In short his point of view is that Stalin is an image, archetype of a father of nation that is imbeeded in Russian mentality irrespective of what actually was historical Stalin and that this archetype is a constant to Russia. He claims that the people want a leader under which the elites will suffer and fear, and Stalin is exactly such leader. He also claims that the popularity of Stalin rises due to comparison with modern leaders.
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P.S. I missed to mention two more serious reasons why Stalin may be popular today based on modern politics.
The first one is that the anti-Russian apartheid regimes in the Baltic states (Estonia, Latvia, Lithuania) and Ukrainian anti-Russian neo-Nazis use attacks on Stalin as a means to justify anti-Russian legislation. If you are against ban on Russian language, you are Stalinist, if you are for equal rights for Russians, you are Stalinist, if you disagree that Stalin was worse than Hitler, you are Stalinist, if you dislike the yearly SS veterans parades, you are Stalinist, if you disagree that anti-Hitler war veterans should be stripped of any pension, you are Stalinist, if you do not support territorial claims to Russia and demands for financial compensation, you are Stalinist. Russians are well aware of this and perceive that if their enemies do not like Stalin, they should do something the opposite.
The fact that the politicians who support many unpopular measures such enforcement of copyright laws and joining controversial international agreements such as ACTA, cooperation with NATO and support for the US foreign policy, easing the anti-corruption laws and de-crimilalization of bribery often at the same time propose anti-Stalinist measures. For example, the recent "presidential commission for de-Stalinization" that was instituted in 2011, is headed by Michail Fedotov, who at the same time the chairman of the Russian Copyright Society, analog of the US RIAA.